Nanoparticle light filtering method and apparatus

ABSTRACT

Implementations of the present invention relate to apparatuses, systems, and methods for blocking, attenuating, or filtering neuroactive wavelengths of the visible light spectrum and reducing or preventing the symptoms affiliated with exposure to those wavelengths. Nanoparticles of a predetermined composition, size, and structure are dispersed in a host medium to create an optical notch filter, thereby attenuating only a narrow range of the visible spectrum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a divisional of U.S. patentapplication Ser. No. 14/542,564 entitled “NANOPARTICLE LIGHT FILTERINGMETHOD AND APPARATUS”, filed Nov. 15, 2014, which claims priority to andis a continuation-in-part of U.S. patent application Ser. No. 14/542,478entitled “NANOPARTICLE LIGHT FILTERING METHOD AND APPARATUS”, filed Nov.14, 2014, which claims priority to and the benefit of U.S. ProvisionalPatent Application Ser. No. 61/904,861 entitled “NANOPARTICLE LIGHTFILTERING METHOD AND APPARATUS”, filed Nov. 15, 2013. All of theaforementioned applications are incorporated herein by reference intheir entirety.

BACKGROUND

Generally, this invention relates to optical filtration. Morespecifically, the present invention relates to the reduction ofphysiologic responses to certain wavelengths of light using notchfilters containing nanoparticles.

Various electromagnetic wavelengths can have physical effect on thehuman body. In particular, certain wavelengths within the visiblespectrum are suspected to have Sa negative neurological effects whenreceived by certain photoreceptors in the human eye. Distinct from therods and cones of the human eye, the melanopsin ganglion cells are alsoknown as intrinsically photoreceptive Retinal Ganglion Cells (ipRGCs)and are intrinsically photoreceptive cells contained in the retina. Thecells are connected to certain pain pathways, as well as connected tothe suprachiasmatic nucleus. The pain pathways of the thalamus aresuspected to affect migraine headaches. Meanwhile, the ipRGCs'interaction with the suprachiasmatic nucleus participates in entrainmentof circadian rhythms.

The melanopsin ganglion cells' interaction with pain pathways of thebrain have been linked to photophobia. In contrast to the common usageof “phobia,” this is not an irrational fear of light, but rather aphysical sensitivity to light. Photophobia has been linked to causing orexacerbating migraine headaches or other light sensitive neurologicalconditions such as blepharospasm and traumatic brain injury (TBI). Theblockage or attenuation of the wavelengths of light that are related tophotophobia may have a number of positive benefits. Reducing photophobiain sensitive individuals may lessen or prevent migraine headaches andother negative health effects.

Circadian rhythms are the internal cycles of the body, whichapproximately synchronize the 24 hour day-night cycles of the earth.Circadian rhythms are important for sleep, moods, and nutrition, as thisinternal cycle determines when one will feel the need to sleep or eat.They can be very beneficial in keeping the body “on schedule,” but mayalso become problematic to individuals who do not want their body toalign with the local daylight schedule. For example, individuals whotravel frequently may be able to avoid the effects of jetlag bypreventing changes to their circadian rhythms due to briefly travelingto a locale in a differing time zone. Alternatively, individuals workingin professions with non-daylight hour based schedules may want to avoidthe effects of the sunlight on their circadian rhythm. For example, adoctor on a night-shift rotation may want to entrain their body with acircadian rhythm irrespective of the light or darkness during the hoursthey may be awake and active.

To block or attenuate the wavelengths that are negatively neuroactive,the current method is to wear lenses that attenuate light across much ofthe visible spectrum. This method, however, has significant detrimentsas the lenses will impair vision in low-light settings and distortcolors in nearly all situations. It would be preferable to attenuate thelight arriving at the eye only within the narrow range or ranges thatare suspected to be neuroactive.

Thus, there are a number of benefits from the selective attenuation orfiltering of neuroactive wavelengths of light that can be realized.

BRIEF SUMMARY

Implementations of the present invention address one or more of theforegoing or other problems in the art with compositions, devices,systems, and methods for blocking, attenuating, or filtering neuroactivewavelengths of the visible light spectrum and reducing or preventing thesymptoms affiliated with exposure to those wavelengths.

In a first non-limiting embodiment incorporating the presently claimedinvention, an optical filter may comprise nanoparticles dispersed in ahost medium. The host medium may then be disposed on a substrate. Thesubstrate may be transparent to light in the visible spectrum such thatthe only attenuation of light is due to the dispersion of nanoparticlesin the host medium coating the surface.

In a second non-limiting embodiment, a method of manufacturing anoptical notch filter comprises determining a desired central wavelengthof the filter, determining a desired full width half maximum of thefilter, and manufacturing the filter by varying a size of a plurality ofnanoparticles, a composition of the nanoparticles, and a composition ofa host medium in which the plurality of nanoparticles are located. Thefilter may be manufactured by a variety of deposition techniquesincluding spin coating and dip coating.

In a third non-limiting embodiment, a method for reducing the frequencyand/or severity of photophobic responses includes receiving an amount oflight across a visible spectrum

Additional features and advantages of exemplary implementations of theinvention will be set forth in the description which follows, and inpart will be obvious from the description, or may be learned by thepractice of such exemplary implementations. The features and advantagesof such implementations may be realized and obtained by means of theinstruments and combinations particularly pointed out in the appendedclaims. These and other features will become more fully apparent fromthe following description and appended claims, or may be learned by thepractice of such exemplary implementations as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. For better understanding, the likeelements have been designated by like reference numbers throughout thevarious accompanying figures. While some of the drawings may beschematic representations, at least some of the drawings may be drawn toscale. Understanding that these drawings depict only typical embodimentsof the invention and are not therefore to be considered to be limitingof its scope, the invention will be described and explained withadditional specificity and detail through the use of the accompanyingdrawings in which:

FIG. 1 is a graph depicting the melanopsin action potential response inrelation to the transmission characteristics of a typical FL-41 35filter prescribed to some patients with a photoresponsive medicalcondition.

FIG. 2 is a graph depicting a typical human visual response spectrum inrelation to the transmission characteristics of a typical FL-41 35filter prescribed to some patients with a photoresponsive medicalcondition.

FIG. 3 is a graph depicting the melanopsin action potential response inrelation to the transmission characteristics of a typical FL-41 55filter prescribed to some patients with a photoresponsive medicalcondition.

FIG. 4 is a graph depicting a typical human visual response spectrum inrelation to the transmission characteristics of a typical FL-41 55filter prescribed to some patients with a photoresponsive medicalcondition.

FIG. 4A is a graph depicting incident angle transmission.

FIG. 5A is a simulated extinction spectrum for a 40 nm sphericalnanoparticle.

FIG. 5B is a simulated extinction spectrum for a 40 nm cubicnanoparticle.

FIG. 5C is a simulated extinction spectrum for a 40 nm tetrahedralnanoparticle.

FIG. 5D is a simulated extinction spectrum for a 40 nm octagonalnanoparticle.

FIG. 5E is a simulated extinction spectrum for a 50 nm triangularnanoparticle that has a 5 nm thickness.

FIG. 5F is a series of simulated extinction spectra for 50 nm widerectangular prism nanoparticles of different axial lengths.

FIG. 5G is a graph depicting simulated extinction efficiencies forspherical particles of different diameters.

FIG. 6 is a schematic cross-sectional view illustration depicting oneembodiment of a light filtering apparatus according to the presentinvention.

FIG. 7 is a schematic cross-sectional view illustration depictinganother embodiment of a light filtering apparatus according to thepresent invention.

FIG. 7A is a graph depicting the measured transmission spectrum for avariety of immersion durations.

FIG. 8 is a cross-sectional view illustration depicting one embodimentof a core-shell nanoparticle and associated spectra in accordance withthe present invention.

FIG. 9 is a cross-sectional view illustration depicting one embodimentof a metallic nanoparticle and associated spectra in accordance with thepresent invention.

FIG. 9A is a plot of simulated extinction efficiencies for sphericalparticles in solution with different media.

FIG. 9B is a plot of simulated extinction efficiencies for particles ofvarying alloying percentages.

FIG. 10 is a flowchart diagram of one method of mitigating aphotoresponsive medical condition in accordance with the presentinvention.

DETAILED DESCRIPTION

One or more implementations of the present invention relate to theproduction of lenses, filters, other devices, or methods of blocking,attenuating, filtering or otherwise regulating the particularwavelengths of light that reach the human eye. In particular, thepresent invention is primarily concerned with the attenuation ofneuroactive wavelengths that affect the melanopsin-containing ganglioncells in the retina of the eye. The melanopsin-containing ganglion cellsare also known as the intrinsically photoreceptive Retinal GanglionCells, or ipRGCs and form the top layer of photoreceptive cells in theretina. When neuroactive wavelengths interact with the ipRGCs,transmissions are sent to a number of locations in the brain, aside fromthe image-processing centers. Included amongst those are the paincenters in the thalamus and the circadian rhythm control center in thesuprachiasmatic nucleus, a collection of neurons in the brain's midline.The present invention is particularly concerned with the filtration orattenuation of the wavelengths that activate at least these nervecenters.

The neuroactive wavelengths can be regulated at the source or near thereceptors in the eye. For example, a coating or filter may be placedacross a screen or lens at the source to prevent the source fromemitting the wavelengths. Alternatively or in addition, an individualmay be able to filter the light approaching their eyes by, for example,wearing glasses that filter or attenuate particular wavelengths. Therecan be environmental considerations that dictate which method ispreferable at the time. In a workplace, a large percentage of theneuroactive wavelengths may be produced simply by a computer monitor infront of an individual. An individual who is sensitive to particularwavelengths may be able to sufficiently reduce their exposure to thatlight by applying a filter to the computer screen directly. Similarly, acoating could be deposited on light bulbs or windows to attenuate thewavelengths at the source when indoors.

However, in another environment, simply reducing the emission of theneuroactive wavelengths at point sources may be insufficient to reducean individual's exposure. For example, it may not be possible to reduceemissions from all sources in a building, or the primary source of theneuroactive wavelengths may be natural or ambient light, such as solar,rendering a source-based solution impossible. In such a situation, asensitive individual may wear or otherwise use a filter adjacent orproximate their ipRGCs. The selective regulation of the wavelengths maybe performed by a transparent surface. The filter may be integral to alens, such as in sunglasses, or merely a coating on a lens, such as athin coating applied to a conventional prescription lens used for visioncorrection. In such a manner, the individual may be able to weareyeglasses or even contact lenses with neuroactive wavelengthattenuating properties and effectively regulate nearly all lightreaching the eye.

FIG. 1 depicts a graph 100 with an example of the estimated actionpotential spectrum for the ipRGCs. The solid points 102 on the graph 100are the empirically measured response values for wavelengths, normalizedto the maximum response, and the dashed line is a Gaussian distribution110 fit to the response data. This Gaussian distribution 110 is notmeant to be representative of the precise response spectrum of theipRGCs, but rather an approximation of the depicted dataset. Morerefined data sets may become available regarding the response spectrumof ipRGCs, and it should be understood that the present disclosure is atleast equally applicable to refined response spectra.

FIG. 1 also depicts the transmission characteristics 120 of the “FL-4135” filter that is, currently, a commonly prescribed filter forregulating the transmission of light to photosensitive individuals inindoor environments. The FL-41 35 filter is created by impregnating amaterial with an organic dye to reduce the transmission of light throughthe material. As shown in FIG. 1, the filter transmits the lowest amountof incoming light at approximately 500 nm wavelengths, but transmitsless than 70% of incoming light from 400 nm to 640 nm, corresponding toviolet through orange colors in the visible light spectrum. Meanwhile,the photoreceptors in the ipRGCs are below a 5% response outside of 430nm to 520 nm, as shown. Therefore, while the amount of light perceived130 by the ipRGCs is significantly reduced by the FL-41 35 filter, theremainder of an individual's vision is also impaired.

This effect is more fully visualized in FIG. 2. The graph 200 in FIG. 2depicts the effect of the transmission characteristics 120 of the FL-4135 filter on an individual's approximate overall visual responsespectrum 210. The estimated effective visual response 230 issignificantly impacted across the full width of the spectrum. In total,a FL-41 35 filter prevents transmission of about 47% of incoming lightin a complete visible spectrum. Blocking the entirety of the visiblelight spectrum can lead to undesired effects such as distortions inperceived colorations and/or may diminish vision in low-light situationsto an unacceptable level for a user. Furthermore, because the reductionin transmission is spread across the spectrum, the FL-41 35 filter isundesirable option when considering coatings for point sources.

FIG. 3 depicts a graph 300 with an example of the estimated actionpotential spectrum 310 for the ipRGCs as inhibited by a FL-41 55filter's transmission characteristic 320. The FL-41 55 is a version ofthe FL-41 35 filter with a higher amount of the transmission-blockingdye impregnated into the material. The FL-41 55 inhibits about 89% oflight transmission in the range in which melanopsin cells are active,but the FL-41 55 filter also inhibits about 81% of the total spectrumfrom passing through the material, as can be seen in FIG. 4, whichincludes the visual response spectrum 210 overlaid. Because it transmitsless light, the FL-41 55 filter is prescribed primarily for outdoorapplications. However, this highlights one of several drawbacks to theFL-41 filter: the associated attenuation of other portions of thespectrum means that a user must change actual FL-41 filter from, forexample a FL-41 35 filter to a FL-41 55 filter when transitioning fromindoor environments to outdoors. Other drawbacks include theaforementioned color distortion and safety concerns in low-lightsituations, the requirement that the dye be mixed with only certaintypes of plastics, and difficulties with uniformity of the tintingprocess.

It is therefore desirable to produce a filter that will attenuate theneuroactive wavelengths while minimizing spectral distortion. Additionalor other constraints on filter design may be considered, includingoptimization methods.

One method to evaluate the performance of optical filters in the contextof blocking light absorption by melanopsin cells is presented here. Thelight dose D experienced by melanopsin cells can be written

D _(melan) =∫L(λ)T(λ)M(λ)dλ

where L is the light spectrum (in terms of intensity, power,photons/sec, etc), T is the spectral transmission of a filter lyingbetween the light source and the eye, and M is the normalized actionpotential response spectrum of melanopsin, as currently estimated fromFIG. 1 as a Gaussian function centered at 480 nm with a full-width athalf-maximum of 52 nm. For generality, it is assumed that L=1 so as notto limit discussion to any specific light source, however analyses maybe performed for any light source of known spectrum. A similar dose canbe calculated associated with the visual response spectrum

D _(vis) =∫L(λ)T(λ)V(λ)dλ

where V represents the normalized visual response spectrum. The effectof an optical filter, such as the FL-41 tint, is to reduce the dose, asdescribed by taking the ratio of dose calculated with the filter to dosewithout the filter. A figure of merit (FOM) can also be defined whichcompares the blocking of the melanopsin response to the blocking of thevisual response spectrum

${FOM} = \frac{1 - \frac{D_{melan}}{D_{melan}\left( {T = 1} \right)}}{1 - \frac{D_{vis}}{D_{vis}\left( {T = 1} \right)}}$

where a value FOM>1 may be desirable. For example, the FL-41 tint mayproduce a value FOM≈1.

As shown in the above FOM equation, the value FOM will increase as thespectrum of the notch filter more closely approximates the visualresponse spectrum of the melanopsin and the ipRGCs. The numerator willapproach 1 as the light dose D_(melan) experienced by melanopsin cellswith a filter approaches 0 when compared against the unfiltered lightdose D_(melan)(T=1). In contrast, the denominator will approach zero asthe filter attenuates a smaller portion of the visible spectrum, thuscausing the value FOM to become greater than 1. A value FOM>1 reflects apreferential filtering wavelengths within the melanopsin visual responsespectrum over the rest of the visible spectrum.

A notch or band-stop filter is one that passes most wavelengths orfrequencies unaltered, but will attenuate those within a narrow range tovery low levels. A notch filter can be thought of as the opposite of aband-pass filter. A notch filter may have a high Q factor, correspondingto a narrow stopband. Optical filter technologies may include, amongother technologies, dielectric multi-layers and nanoparticle coatings.The latter may include metallic nanoparticles, dielectric nanoparticles,semiconductor nanoparticles or quantum dots, magnetic nanoparticles,core-shell particles consisting of one material in the core and anotherserving as a shell. The nanoparticles may have a variety of shapes. Hostmaterials may include polymers, sol-gels, glasses or similar transparentor translucent materials.

The use of nanoparticles for wavelength attenuation has propertiesdistinct from thin-film methods because the nanoparticles will scatterand absorb light irrespective of the incident angle of the light, asshown in graph 440 in FIG. 4A. The variation between the measuredtransmission of incident light that is normal 450 a, 30° 450 b, and 60°450 c to a surface of the filter, may be at least partially due todouble interface reflection of 8%, 12%, and 31%, respectively for theoptical filter. The double interface reflection coefficient may becalculated accruing to Fresnel equations. The calculated doubleinterface reflection coefficients are in agreement with the measuredtransmission spectra. Because a nanoparticle notch filter will performpredictably regardless of the direction of light source, it is wellsuited for general purpose filtering, such as with eyeglass lenses.Furthermore, to accomplish the proper scattering and absorption oflight, a number of parameters may be varied to optimize the range ofwavelengths attenuated and the amount of attenuation and to tune thenotch filter to different wavelengths.

A metallic nanoparticle may be excited by an incident light or otherelectromagnetic (“EM”) radiation. The excitation of the metallicnanoparticle may result in the metallic nanoparticles exhibiting acollective oscillation of conduction electrons. A charge densityoscillation of the conduction electrons is a localized surface plasmon(“LSP”). The LSP may enhance local electromagnetic fields duringresonance of a plurality of LSPs excited by an incident selectivewavelength of light. The resonant behavior of a plurality of LSPs isknown localized surface plasmon resonance (“LSPR”). LSPR may providelarge optical field enhancement and may lead to strong scattering and/orabsorption of the incident wavelength. In simplified form, the frequencyat which LSPR occurs may be given by:

$\omega_{LSPR} = \frac{\omega_{p}}{\left( {1 + {2ɛ_{d}}} \right)^{1/2}}$

where ω_(LSPR) is the frequency at localized surface plasmon resonance,ω_(p) is the plasmon frequency of the metal and ε_(d) is the dielectricconstant of the environment surrounding the metallic nanoparticles. TheLSPR wavelength and the peak width of the nanoparticle optical responsemay be sensitive to at least nanoparticle composition, size, shape,dielectric environment, proximity to other nanoparticles, orcombinations thereof.

There may be scattering and absorption of incident light due to the highlocal field enhancement at the surface of nanoparticle at LSPR. Thescattering of the light may be explained as the redirection of lightthat takes place when an electromagnetic (EM) wave encounters anobstacle (i.e., a nanoparticle). The absorption of the light can beexplained by the amount of the incident light energy absorbed by thenanoparticle in the form of heat. The attenuation or loss of incidentlight through the combination of scattering and absorption of light isextinction. Nanoparticle dispersion on or within a transparent mediummay allow for increased extinction at a variety of angles and amounts ofincident light.

The extinction spectrum of a dispersion of nanoparticles may be modeledby a combination of approximations. Quasi static approximation may allowfor modeling of the scattering and absorption coefficients of sphericaldimension of size less than 1% of the wavelength of the incident light.Mie scattering theory (or Mie Theory) may provide approximations of thescattering and absorption coefficients of nanoparticles of other shapesand/or sizes. Mie Theory may provide a general framework enabling theexact solution to the scattering and absorption of light of a sphericalparticle.

As shown in FIGS. 5A-5F, the shape of a nanoparticle can have an effecton its extinction spectrum. A spherical particle spectrum 510,calculated based on spherical silver (Ag) nanoparticles having a 40 nmdiameter, may have the most focused spectrum of the presentedembodiments because they have a single, narrow primary peak that allowsfor optimization using size and composition changes, as shown in FIG.5A. However, it may be possible to utilize a combination of particles ofother shapes in order to develop a desired filter spectrum. In someembodiments, one may broaden the extinction spectrum of a 40 nmspherical nanoparticle filter by simply introducing, for example, 40 nmcubic nanoparticles or 40 nm octahedral nanoparticles. For example, FIG.5B depicts a cubic particle spectrum 520 calculated based on cubic Agnanoparticles having a 40 nm width. FIG. 5C depicts a tetrahedralparticle spectrum 530 calculated based on tetrahedral Ag nanoparticleshaving a 40 nm width. FIG. 5D depicts an octahedral particle spectrum540 calculated based on octahedral Ag nanoparticles having a 40 nm widthalong each edge. In other embodiments, one may introduce a second peakat a longer wavelength by introducing, for example, triangular platenanoparticles. FIG. 5E depicts a triangular particle spectrum 550calculated based on triangular plate Ag nanoparticles having a 40 nmwidth along the long edges and a thickness of 5 nm. The usage of varyingparticle shapes may be beneficial in tuning a spectrum of thenanoparticle filter. FIG. 5F depicts the extinction spectra of a 50 nmwide Ag prism with varying axial lengths. The longest axial length hasthe longest wavelength extinction spectrum 560, the medium axial lengthhas the medium wavelength extinction spectrum 562, and the shortestaxial length has the shortest wavelength extinction spectrum 564.

FIG. 5G depicts the simulated extinction spectrum for a sphericalparticle using Mie scattering theory for 20 nm, 60 nm, 120 nm, and 240nm Ag particles. As one increases the diameter of a sphericalnanoparticle, the spectral response may red-shift (moves towards alonger wavelength), the peak may broaden, and a higher order resonancemode at a shorter wavelength may become more pronounced. When thedimensions of the particle become comparable with to the wavelength ofthe light, the spectral position of the LSPR may red-shift with respectto that predicted by the electrostatic theory. A particle withdimensions closer to that of the incident wavelength of light mayexperience a retarded field, because the incident EM field is notcontinuous across the spherical particle, further leading toinhomogeneous polarization of the nanoparticle. The inhomogeneouspolarization of the nanoparticle may lead to the excitation of thehigher order resonant modes 570 visible in FIG. 5G. Therefore, it isbeneficial to use particles less than about 100 nm in diameter, and evenmore preferable to use nanoparticles less than about 80 nm in diameter.

An ambient host material may also affect the extinction spectrum of thenanoparticle dispersion and an associated optical filter. For example,the scattering coefficients may be proportional to the relative index ofthe refraction of the host material. The position of the extinctionspectrum may be at least partially dependent on the dielectric constantof the host material. As the refractive index of the host material inwhich the nanoparticles are embedded is increased, the spectral positionof the LSPR red shifts, which may result in a narrower and greaterextinction coefficient.

In an embodiment, a filter according to the present invention may usenanoparticles that absorb or reflect light in a narrow range toeffectively block only that range of wavelengths. In an embodiment, thenanoparticles may be distributed in a bulk transparent host material. Inanother embodiment, the nanoparticles may be distributed within atransparent host material applied as a coating on a substrate. Thesubstrate may be transparent, as well. For example, as shown in FIG. 6,the nanoparticles 620 may be distributed in a host material 610, or asshown in FIG. 7, the nanoparticles 720 may be suspended in a coating 710deposited onto the surface of a substrate 750.

In FIG. 6, the nanoparticles 620 are depicted suspended in a hostmaterial 610 that is otherwise transparent to the visible spectrum.Therefore, the host material 610 itself attenuates none of the visiblelight and allows full or nearly full transmission of the visiblespectrum. Therefore, the only effects on light attempting to passthrough the host material 610 are due to the nanoparticles 620. In someembodiments, the nanoparticles 620 may be distributed substantiallyevenly throughout the host material 610. In other embodiments, thenanoparticles 620 may agglomerate, resulting in uneven distributions.For example, Ag nanoparticles may agglomerate when in solution, formingcluster of a nanoparticles that, in effect, act as larger particlesaffecting the LSPR behavior. The nanoparticles 620 may include adeagglomeration coating thereon to limit the agglomeration of thenanoparticles. The solution in which the nanoparticles 620 are dispersedmay also include a deagglomeration agent.

Likewise, the host material may be a coating 710 that may be, along withsubstrate 750, substantially transparent to the visible spectrum, asdepicted in FIG. 7. In either situation, the host material 610, coating710, substrate 750, or similar structures may be transparent or haveindependent light filtering or blocking characteristics. Thenanoparticles 720 may agglomerate or otherwise cluster together duringthe application of the nanoparticles 720 and coating 710 to thesubstrate 750. To limit or, in some cases, prevent the clustering of thenanoparticles 720, the coating 710 may be applied in a thin film. Insome embodiments, the thin film coating 710 may be applied to thesubstrate 750 by spin coating. Spin coating may allow the deposition ofa uniform thickness of the coating 710 and nanoparticles 720 across thesurface of the substrate 750. In other embodiments, the coating 710 maybe applied to the substrate 750 by dip coating.

Spin coating creates a thin substantially uniform coating 710 byspinning the substrate 750 during application of the coating 710. Thespinning of the substrate may cause the fluid coating 710 (and suspendednanoparticles 720) to move in a circular motion. The circular motion mayprovide the coating 710 and suspended nanoparticles 720 with inertiathat urges the coating 710 and suspended nanoparticles 720 radiallyoutward from a rotational axis. The force applied outward (commonlyknown as “centrifugal force”) may be given by:

F _(c) =m×r×ω ²

where F_(c) is the centrifugal force, m is the mass of the coating, r isthe distance from the rotational axis, and ω is the angular velocity inradians per second. The thickness of the coating 710 may decrease withincreasing force and, therefore, with mass and the square of the angularvelocity.

Dip coating may create a thicker coating 710 than spin coating byimmersing the substrate 750 in a solution including suspendednanoparticles 720 for a period of time and then withdrawing thesubstrate from 750 from the solution. The thickness of the coating maybe at least partially dependent upon the duration of the immersion, therate of withdrawal of the substrate 750, and the viscosity of thesolution. For example, a longer immersion in the solution may allow fora thinner the coating 710 that is deposited onto the substrate 750. Theconcentration of the nanoparticles 720 within the coating 710 mayincrease with longer immersion times. In another example, a fasterwithdrawal rate may decrease the thickness of coating 710 on thesubstrate 750.

As shown in FIG. 7A, when employing, by way of example but withoutlimitation, Ag nanoparticles having a major dimension of about 70 nm,the overall transmission of a filter increases as the duration ofimmersion increases. The thinner coating 710 allows a greater percentageof the incident light to be transmitted. FIG. 7A depicts thetransmission spectrum of a 10 second, 30 second, 60 second, and 120second immersion of a glass slide in PVA dissolved Ag nanoparticlesolution. The Ag nanoparticles suspended in solution may be about 70 nmin diameter. In other embodiments, the nanoparticles may have otherdiameters and exhibit similar behavior. The 10 second immersion curve760 a may result in a lower overall transmission of light through thefilter. The overall transmission may increase and the 120 secondimmersion curve 760 b may transmit more overall light.

In an embodiment, it may be beneficial for a coating of nanoparticlesintended to regulate neuroactive wavelengths be disposed within or upona surface of a material, coating or substrate containing dye to reducethe transmission of light, such as in traditional sunglasses lenses. Insuch a situation, the dye may be chosen independently of its neuroactivewavelength regulating properties while the layered structure would stillprovide the aforementioned neurological benefits. In another embodiment,the material, coating, or substrate material may include other desirableadditions, such as photochromic components. For example, this may resultin a lens for eyeglasses that may alter its transmission characteristicsacross some or substantially all of the visible spectrum whilemaintaining optimal attenuation of the neuroactive wavelengths.Therefore, such a lens would be appropriate for use indoors or out.

Also depicted in FIGS. 6 and 7 are graphs 600, 700 with spectrarepresentative of daylight at sea level of the incident light 630, 730and the simulated transmitted light 640, 740 for the host material 610with suspended nanoparticles 620 and the coating 710 with nanoparticles720, respectively. In this example, the nanoparticles scatter and/orabsorb wavelengths in the 480 nm range. In an embodiment, the opticalnotch filter may attenuate the target wavelength, such as 480 nm, andabout 25 nm greater and less than the target wavelength, measured as afull-width half-maximum (“FWHM”) of about 50 nm. In another embodiment,the notch filter may have a FWHM of about 50 nm to about 80 nm. In yetanother embodiment, the notch filter may have a FWHM of less than about100 nm. 480 nm is the wavelength that generates the maximum responsefrom the ipRCGs; however, dispersed nanoparticles can regulate thetransmission of other wavelengths, such as 590 nm or 620 nm, as well. Inan embodiment, the nanoparticles may have a major dimension less thanabout 80 nm. In another embodiment, the nanoparticles may have a majordimension less than about 72 nm. In yet another embodiment, thenanoparticles may have a major dimension less than about 50 nm.

Referring now to FIG. 8, a core-shell nanoparticle 800 is shown havingan inner core 810 with an outer shell 820. The depicted core-shellnanoparticle 800 is substantially spherical, but in other embodiments, acore-shell nanoparticle may have cross-sections including a circle, anellipse, a rectangle, a hexagon, an octagon, or other polygon. The coreand shell of the nanoparticle may differ in composition. In someembodiments, the inner core 810 may comprise one or more materialsselected from a group consisting of a metal, a dielectric material, anda magnetic material. The inner core 810 may comprise a noble metal, atransition metal, a post transition metal, an alkali metal, or analkaline earth metal. The noble metal may be silver, gold, or platinum.The transition metal may be copper, titanium, or zinc. Thepost-transition metal may be aluminum or gallium. The alkali metal maybe sodium or potassium. The alkaline earth metal may be magnesium. Theinner core 810 may also comprise an alloy of two or more of theaforementioned metals. In other embodiments, the inner core 810 maycomprise a metal oxide, including SiO₂, TiO₂, Al₂O₃, or ZnO.

Likewise, any of the aforementioned metals, dielectric materials, ormagnetic materials may be suitable as a material for the outer shell820, as well. In some embodiments, the core may comprise SiO₂ and theouter shell 820 may comprise silver (Ag). In other embodiments, thecore-shell nanoparticle 800 may comprise SiO₂ and Ag, where the SiO₂ isthe material of the inner core 810 and accounts for about 58% of theradius. The remaining 42% of the radius is the Ag outer shell 820. Thecore-shell nanoparticle 800 may have other ratios between the inner core810 and the outer shell 820, however, to tune the spectral response. Inyet another embodiment, the inner core 810 may have a thickness of 16nm. In a yet further embodiment, the outer shell 820 may have athickness of 8 nm.

The extinction spectrum of a spherical nanoparticle may be calculatedusing the Mie scattering theory, which is partially dependent uponradius of the core-shell nanoparticle 800. As described in relation toFIG. 5G, the radius of a nanoparticle, therefore, can be used tofine-tune the spectral response 830 of the nanoparticle filter. In someembodiments, given a constant composition of the nanoparticles withinthe optical filter, the extinction spectrum of the filter may shifttoward a longer wavelength with a larger average radius of thenanoparticles. In other embodiments, a larger average radius of thenanoparticles may attenuate a larger portion of the light.

In contrast to FIG. 5G, FIG. 8 depicts the effect of altering the radiusof the core of a core-shell nanoparticle 800. There is little or noshift in the notch position, but rather only the amplitude anddistribution of the curve about the peak position. Such a change in thedistribution of material in the core-shell nanoparticle 800 may allowfor the optimization of a notch filter by varying the amount of lightattenuated without necessitating a change in medium or a change in sizeof the core-shell nanoparticles 800.

Furthermore, the density of the nanoparticles suspended in the materialmay be selected to achieve the desired rate of attenuation of theneuroactive wavelengths. One of skill in the art will understand that ahigher density of nanoparticles will provide a higher rate ofattenuation, but one may only increase attenuation rates this way untilfurther concentration would lead to coupling of resonances betweenparticles. To prevent agglomeration of the nanoparticles, thenanoparticles may include an anti-agglomeration shell or coating asdescribed in relation to FIG. 6, such as polyvinylpyrrolidone.

The nanoparticles may be in solution with the host medium. The hostmedium may be a polymer suspension, such as polyvinylacetate,polymethylmethacrylate (PMMA), sol-gel, or similar medium. In anembodiment, the concentration of nanoparticles in the solution with thehost medium is about 15% weight to volume. In another embodiment, theconcentration of nanoparticles in the solution with the host medium isabout 20% weight to volume. In yet another embodiment, the concentrationof nanoparticles in the solution with the host medium is about 7.05×10¹⁰particles per cubic centimeter. In a yet further embodiment,nanoparticles in the solution with the host medium may have a molecularweight of between 30,000 and 100,000.

Additionally, the medium selected for the bulk material or coatingmaterial in which the nanoparticles are suspended will shift theresponse spectrum. Referring now to FIG. 9, a nanosphere 900 is showncomprising a single material 910 with a radius 920. In an embodiment,the nanosphere 900 may comprise one or more of the materials describedfor use in the inner core 810 of a core-shell nanoparticle 800 mentionedabove. The spectral responses of 15 nm Ag nanospheres 930 a and 25 nm Agnanospheres 930 b are dependent on both the index of refraction of thebulk material or coating medium in which the nanosphere is suspended.FIG. 9a depicts the effect of medium refractive index on the simulatedspectral response of a spherical 30 nm Ag nanoparticle. As therefractive index of the medium increases, the wavelength attenuated bythe notch filter increases. In various embodiments, the index ofrefraction of the medium may be less than about 1.5, about 1.5, orgreater than about 1.5. As discussed earlier, an increase in the radiusof the nanosphere results in increased attenuation, but also shifts thespectral response. However, a change in the index of refraction of themedium enables the spectral response to be shifted back toward thedesired wavelength, in this case, 480 nm.

A nanoparticle 900 with a single radius 910 (i.e., a substantiallyhomogenous nanoparticle) may exhibit a variety of extinctioncoefficients. Varying the alloying percentage of materials in thenanoparticle 900 while maintaining a constant radius 910 may shift thewavelength attenuated by a notch filter. For example, FIG. 9B is a graphillustrating the effects of variations in alloying percentage of ananoparticle including a silver-aluminum alloy metal (AgXXAlXX, where XXis a percentage composition). The coefficient of extinction for eachcomposition may blue-shift as the percentage of aluminum in the alloyincreases. For example, the Ag90Al10 curve 950 a has a local maximum atabout 400 nm, and the Ag50Al50 curve 950 b has a local maximum at about320 nm.

It should be understood that the examples thus far have described anoptical notch filter comprising a unimodal distribution of nanoparticlesin order to attain a high Q factor and attenuate a single wavelength ornarrow range of wavelengths. However, the use of an optical notch filteris not exclusive to one wavelength, and the use of nanoparticles ofdifferent shapes, compositions, or sizes is possible for the selectiveattenuation of more than one wavelength.

This may be accomplished either by homogenous dispersion ofnanoparticles with more than one composition, shape, and/or size, or bylayering of coating materials with one or more particular species ofnanoparticle. For example, a filter may be produced with the 25 nm Agnanospheres of FIG. 8 to attenuate light in the 480 nm range of thespectrum with other nanoparticles appropriate to attenuate light inanother range of the spectrum, each of the species distributedhomogenously. Alternatively, a first coating appropriate for attenuatinglight in a first range, such as the 480 nm range, could be applied tosurface of an eyeglasses lens, while a second coating appropriate forattenuating light in a second range could then be applied to anothersurface of the lens or layered on top of the first coating. Whetherapplied singularly or in combinations, each coating may have a thicknessgreater than about 5 μm. In another embodiment, the coating may have athickness of about 6 μm. In another embodiment, the coating may have athickness of about 11 μm.

The thickness of the coating and the distribution of nanoparticleswithin the coating may be controlled by the deposition method of thecoating. In an embodiment, the application of the coating may comprise aspin coating step. In another embodiment, the application of the coatingmay comprise a dip coating step. In yet another embodiment, theapplication of the coating may comprise a deagglomeration step, which,itself, may comprise ultrasonic dispersion.

FIG. 10 depicts a method 1000 of producing an optical notch filter toreduce or alleviate symptoms affiliated with exposure to neuroactivewavelengths. As shown, the method includes at least obtaining 1010 ahost medium and embedding or applying 1020 nanoparticles therein orthereon that filter light corresponding to the action potential spectrumof the melanopsin pathway. Additional steps of the method may includedetermining a desired central frequency of the filter, determining adesired full width half maximum of the filter, or varying the size ofthe plurality or composition of the nanoparticles. In addition, themanufacturing process may include varying the composition of the hostmedium. Depending on the host medium used, the method of manufacture mayoptionally include removing bubbles from a solution of the host mediumand nanoparticles.

The articles “a,” “an,” and “the” are intended to mean that there areone or more of the elements in the preceding descriptions. The terms“comprising,” “including,” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements. Additionally, it should be understood that references to “oneembodiment” or “an embodiment” of the present disclosure are notintended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Numbers,percentages, ratios, or other values stated herein are intended toinclude that value, and also other values that are “about” or“approximately” the stated value, as would be appreciated by one ofordinary skill in the art encompassed by embodiments of the presentdisclosure. A stated value should therefore be interpreted broadlyenough to encompass values that are at least close enough to the statedvalue to perform a desired function or achieve a desired result. Thestated values include at least the variation to be expected in asuitable manufacturing or production process, and may include valuesthat are within 5%, within 1%, within 0.1%, or within 0.01% of a statedvalue.

A person having ordinary skill in the art should realize in view of thepresent disclosure that equivalent constructions do not depart from thespirit and scope of the present disclosure, and that various changes,substitutions, and alterations may be made to embodiments disclosedherein without departing from the spirit and scope of the presentdisclosure. Equivalent constructions, including functional“means-plus-function” clauses are intended to cover the structuresdescribed herein as performing the recited function, including bothstructural equivalents that operate in the same manner, and equivalentstructures that provide the same function. It is the express intentionof the applicant not to invoke means-plus-function or other functionalclaiming for any claim except for those in which the words ‘means for’appear together with an associated function. Each addition, deletion,and modification to the embodiments that falls within the meaning andscope of the claims is to be embraced by the claims.

The terms “approximately,” “about,” and “substantially” as used hereinrepresent an amount close to the stated amount that still performs adesired function or achieves a desired result. For example, the terms“approximately,” “about,” and “substantially” may refer to an amountthat is within less than 5% of, within less than 1% of, within less than0.1% of, and within less than 0.01% of a stated amount. Further, itshould be understood that any directions or reference frames in thepreceding description are merely relative directions or movements. Forexample, any references to “up” and “down” or “above” or “below” aremerely descriptive of the relative position or movement of the relatedelements.

The present disclosure may be embodied in other specific forms withoutdeparting from its spirit or characteristics. The described embodimentsare to be considered as illustrative and not restrictive. The scope ofthe disclosure is, therefore, indicated by the appended claims ratherthan by the foregoing description. Changes that come within the meaningand range of equivalency of the claims are to be embraced within theirscope.

What is claimed is:
 1. A method for reducing the frequency and/orseverity of photophobic responses, including migraine headache, lightsensitivity associated with traumatic brain injury, and blepharospasm orfor modulating circadian cycles, the method comprising: receiving anamount of light across a visible spectrum; introducing an optical filterto the path of the light, the optical filter comprising a plurality ofnanoparticles dispersed within a host material; and attenuating aportion of the spectrum associated with absorption by melanopsinganglion cells such that a figure of merit greater than 1 is achieved,wherein the figure of merit is defined as a ratio of attenuation oflight weighted across an action potential spectrum of a melanopsinpathway to attenuation of light weighted across a visual spectralresponse.
 2. The method of claim 1, wherein the plurality ofnanoparticles exhibit local surface plasmon resonance when exposed tothe portion of the spectrum associated with absorption by melanopsinganglion cells.
 3. The method of claim 1, wherein attenuating a portionof the spectrum comprises attenuating light having a central wavelengthof 480 nm, 590 nm, or 620 nm.
 4. The method of claim 3, wherein theoptical filter has a full width half maximum of less than 100 nm at thecentral wavelength.
 5. The method of claim 3, wherein the optical filterhas a full width half maximum of greater than 50 nm and less than 100 nmat the central wavelength.
 6. The method of claim 3, wherein the opticalfilter has a full width half maximum of greater than 50 nm and less than80 nm at the central wavelength.
 7. The method of claim 1, wherein afigure of merit greater than 1.5 is achieved.
 8. The method of claim 1,wherein a concentration of the plurality of nanoparticles in the hostmaterial is: about 15% weight to volume; about 20% weight to volume; orabout 7.05×10¹⁰ particles per cubic centimeter.
 9. The method of claim1, wherein the concentration of the plurality of nanoparticles in thehost material is about 7.05×10¹⁰ particles per cubic centimeter.
 10. Amethod for reducing the frequency and/or severity of photophobicresponses, including migraine headache, light sensitivity associatedwith traumatic brain injury, and blepharospasm or for modulatingcircadian cycles, the method comprising: receiving an amount of lightacross a visible spectrum; introducing an optical filter to the path ofthe light, the optical filter comprising a plurality of nanoparticlesdispersed within a host material such that the optical filter isconfigured to attenuation light having a central wavelength of 480 nm,590 nm, or 620 nm; and attenuating light at the central wavelength suchthat a figure of merit greater than 1.5 is achieved, wherein the figureof merit is defined as a ratio of attenuation of light weighted acrossan action potential spectrum of a melanopsin pathway to attenuation oflight weighted across a visual spectral response.
 11. The method ofclaim 10, wherein the optical filter has a full width half maximum ofgreater than 50 nm and less than 100 nm at the central wavelength. 12.The method of claim 10, wherein the optical filter has a full width halfmaximum of 80 nm at the central wavelength.
 13. The method of claim 10,wherein a concentration of the plurality of nanoparticles in the hostmedium of about 15% to 20% weight to volume.
 14. An optical filter,comprising: an optically transparent substrate; a host material; and aplurality of nanoparticles incorporated into the host material andapplied to the substrate as a coating, the plurality of nanoparticleshaving an average major dimension of less than 120 nm, wherein thesubstrate, the host material, and the nanoparticles cooperate to providean attenuation spectrum having a central wavelength of 480 nm, 590 nm,or 620 nm, the attenuation spectrum having a full width half maximum ofgreater than 50 nm and less than 100 nm about the central wavelength.15. The optical filter of claim 14, wherein the nanoparticles compriseat least one material selected from the group consisting of a noblemetal, a transition metal, a post transition metal, an alkali metal, analkaline earth metal.
 16. The optical filter of claim 14, wherein thenanoparticles are spherically shaped.
 17. The optical filter of claim14, wherein the plurality of nanoparticles includes at least onecore-shell nanoparticle having an outer shell and an inner core.
 18. Theoptical filter of claim 17, wherein the shell of the core-shellnanoparticle has a thickness of 8 nm.
 19. The optical filter of claim17, wherein the inner core of the core-shell nanoparticle is formed of ametal oxide.
 20. The optical filter of claim 14, wherein the hostmaterial has a predetermined refractive index that is greater than 1.5.